It doesn't matter though because a spy guard can't do anything with a disguise. Let's say he does happen to get one, what is he going to do with it? Recon over prisoners is out of the question since pretty much any guard that's in or near a horde of prisoners will get murdered in a few seconds. The spy can't kill anyone without sacrificing his disguise regardless. Every prisoner is going to figure out he's a spy very quickly since he's a prisoner ignoring orders and chilling with guards. I don't see how it gives the guards any unnecessary advantages against prisoners.